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DATEDIFF() and Month Boundaries

Deb Melkin fed the mogwai after midnight:

I was working on a query this week that reminded me of a fun quirk when working with dates and the DATEDIFF function in particular.

I have a process that takes a while to run. Because of all of the moving parts to keep track of, I have an audit table to track what I’m doing to collect basic info like when did it start, when did it end, etc. I created a simple report for myself to break things down so I can report back to the team. I threw together a simple SQL statement, using DATEDIFF to figure out the how long things took. Looking at the results, I saw some interesting results.

Read on for two queries, one which has a bit of a problem and one which strives to correct that problem.